1. Field of the Invention
The invention relates a drive arrangement for a spring-loaded roller curtain, which is wound on a horizontally mounted drum.
2. Description of the Related Art
Roller curtains for covering large openings such as hallways and open walls in buildings are well known. As used herein the term “roller curtain” will be understood to mean a plurality of slats that are hinged together so that the curtain can be wound on a drum. Such slats may be either insulated or uninsulated, and the gauge of the metal may vary depending on the application, e.g. as acoustical barriers or fire doors. Hinging and mounting arrangements are well known and will not be discussed herein.
A roller curtain is typically wound on a drum by driving the drum in rotation using an electric motor. Counter-balance systems employing torsionally loaded coil springs are well known for reducing the torque necessary to rotate the drum, especially for a vertical coiling type door. For doors that are particularly large and heavy, counterbalance systems employing several sets of concentrically arranged coil springs are necessary.
The springs are chosen and arranged so that the door is nearly “weightless” when closed. For a large door, this may require several sets of springs arranged axially, with concentrically arranged springs in each set.
While the force provided by the springs decreases as the drum rotates and the curtain is raised, the weight of the hanging curtain also decreases as the curtain is wound on the drum. However, the decreasing weight is somewhat offset by the increasing effective diameter of the drum, which increases the moment arm. The system is preferably engineered so that the load on the motors is as uniform as possible as the door curtain is lowered or raised.
Notwithstanding the use of a counterbalance spring system, the load on the motor can still cover a substantial range, particularly for a large door. For example, on a roller curtain-type rated fire door that is 50 feet wide and 20 feet high, the torque output required to raise the door could be in a range of 38,000 in-lb to 90,000 in-lb.